The present invention relates to a knot joint for network structures and particularly to a polyvalent knot joint for spatial network structures.
It is known that by spatial network system it is meant the modular and space coordinated assembly, according to rational geometrical criteria, of standardized construction units having a differentiated strength and a selected typical conformation. The fulcrum of any network system is the knot joint which receives and joins to each other a number of rectilinear beams converging in the joint itself in order to build as rigid a structure assembly as possible.
There are at present many types of knot joints. For example there are joints provided with spherical or spheroidal cores, hemispherical joints, or joints comprising a polygonal round ring, single elements capable of being assembled together, clamping plates or jaws, tube lengths fixed to spherical cores, rods welded in situ to base couplings, etc. Among them all, one of the most spread joints is the one known under the trademark "Mero" which particularly puts into practice the known art the most relevant to the present invention.
The above joint consists of a substantially solid spheroid machined so as to define faces forming angles of 45.degree. and 90.degree. on the surface thereof. In the middle of each of said faces a threaded hole is worked in which the threaded ends of differently sized rods can be screwed. In theory the screwing only aims at preventing the rods from slipping off and the latter must act as struts engaging said spheroid by compression. In order to allow that several rods can converge towards the same spheroid, said rods are greatly tapered at their ends so that a relatively reduced abutment surface is provided.
Knot joints of this type can give good results in achieving either flat or spatial network structures. However they have some important drawbacks.
In fact the knots thus obtained engage their respective rods so that hinges rather than restrained fixings are obtained and in these network structures it is advisable to have as rigid restrained fixings as possible close to the knots, which allows the rods to be lighter in weight or longer. Furthermore the knot is expensive owing to the fact that several workings have to be carried out on the spheroid and at the end of the rods. Also the cost is a consequence of the fact that the knot is arranged for attachments all of the same type on each spheroid. As a result, the attachments and the rod-shaped elements that will be subjected to lower stresses have to be oversized. Furthermore, different technical solutions involve the accomplishment of highly expensive special knots as they have to be planned and carried out in a specific manner.
The last mentioned aspect of the known art is important as it highly limits the activity of a designer who is obliged to respect the characteristics peculiar to these knots. Anyway no solutions that are very different from the standardized ones are possible owing to the fact that when the rods are too near each other, too small compression or abutment surfaces are created and it is known that screw elements must not undergo shearing stresses.